Process for crystallizing dextrose



1968 M. 1.. E. VAN TITTELBOOM 3,406,045

PROCESS FOR CRYSTALLIZING DEXTROSE Filed May 4, 1965 fm/enib r:-

ffarcellfi vanfiliielboom I United States Patent 3,406,046 PROCESS FOR CRYSTALLIZING DEXT ROSE Marcel L. E. van Tittelboom, Sas van Gent, Netherlands,

This invention relates to a new and improved method for obtaining dextrose crystals consisting essentially of dextrose hydrate, from dextrose containing liquors, particularly, such as are produced by the enzymic hydrolysis of starch.

The main object of the invention is to provide a method for obtaining dextrose crystals consisting essentially of dextrose hydrate from the aforementioned dextrose containing liquors wherein the entire dextrose liquor is crystallized without formation of mother liquor. This new method eliminates the crystallizers, resulting in the fact that it also permits the elimination of the step of centrifuging the crystals to separate them from the mother liquor, as currently practiced, and reprocessing the mother liquor for additional yields of dextrose. Other objects Will appear hereinafter.

The present invention provides a process for obtaining dextrose crystals, substantially all of which are in the hydrate form, from a dextrose containing liquor by first forming a thin layer of the liquor on agglomerates of dextrose crystals. A convenient way to accomplish this is to spray the liquor onto the agglomerates. Thereafter, the wetted agglomerates are contacted with dextrose particles which have a predetermined temperature, e.g., the agglomerates are coated with a thin layer of dextrose crystals. The contact of the crystals (which act as seed) with the wetted agglomerates results in substantially instantaneous crystallization of a substantial amount of the dextrose in the film and the agglomerates become free-flowing and substantially free of stickiness. The above operation may be repeated several times in order to crystallize a large amount of dextrose liquor. Because of the high rate of crystallization of the dextrose at the temperature used, a substantial proportion of the crystals is believed to be in the anhydrous form. The agglomerates now coated with a layer of a mixture of anhydrous and hydrate crystals are then subjected to a treatment or conditioning to complete crystallization of the dextrose in the film or liquor and to convert substantially all of the anhydrous crystals present in the layer or film to the hydrate form.

In carrying out the invention, any dextrosecontaining liquor which is supersaturated with respect to dextrose and which contains about 75 to about 88 percent, dry substance, may be used. The liquor to which the invention is particularly applicable is the total hydrolysate obtained by the enzymic hydrolysis of starch. Such liquors are well known in the industry and have concentrations of dextrose of about 90 percent to about 100 percent, dry basis.

The dextrose liquor which is used for Wetting the agglomerates should have a temperature within the range of about 60 to about 80 C. during its application in order to spray it conveniently and evenly onto the agglomerates. Temperatures as low as 45 C. may be used also, but more care must be exercised in handling. It is advantageous to beat air into the liquor to speed up crystallization of the dextrose therein when it is applied to the agglomerates.

The temperature of the agglomerates during the wetting operation and coating with dextrose particles should be maintained within the range of about 15 to about 45 C., 15 to 30 C. being preferred.

3,406,046 Patented Oct. 15, 1968 The dextrose particles used for the coating or seeding should consist predominantly of crystals in the hydrate form.

The agglomerates which are to be treated may vary in size from that of dextrose crystals to small pellets. However, for practical operations, the size should not exceed about 10 mm. in diameter since it is diflicult to grind agglomerates which are larger in size. The preferred size of the agglomerates is about 2 to 4 mm. in diameter.

The amount of liquor sprayed onto the agglomerates in each application may vary, the main limiting factor being to prevent stickiness to such a degree that the agglomerates cannot be handled etficiently. For practical operating conditions, the amount of liquor used for each wetting should be about 20 to about 33 percent, by weight, of the agglomerates, dry basis. If more than about 33 percent of liquor is used, the agglomerates will be difiicult to handle due to stickiness. Similarly, the amount of dextrose particles used as seed in each application may vary but about 20 to about 33 percent, by weight, of the wetted agglomerates, dry basis, gives the most satisfactory results.

After the agglomerates have been wetted and coated or seeded with the dextrose particles, they are preferably subjected to a treatment, which I shall refer to as conditioning, to permit complete crystallization of the dextrose in the film of liquor and to convert substantially all of the anhydrous crystals, if present, to the hydrate form. This may be accomplished by slowly agitating the agglomerates, in one or more stages, in suitable equipment. Generally, a period of time of about 2 to 4 hours is sufficient although this may vary depending, for example, upon the amount of agglomerates and anhydrous crystals present. During this time, the moisture content of the product should be maintained at about 8.5 percent to about 13 percent and the temperature should be maintained within the range of about 15 to 30 C. Good results may be obtained when the relative humidity of the atmosphere in the conditioning unit is within the range of about 70 to percent.

The agglomerates resulting from the foregoing treatment may be passed through grinding or crushing rolls to produce material having the desired size for recycling. The remaining portion is subjected to an additional grinding operation to obtain the desired particle size for final end use.

In order to operate the invention in the most eflicient manner, it is necessary to repeat the application of the thin film of dextrose liquor and also the dextrose particles to the agglomerates several times. The amount of liquor which can be crystallized in a single stage operation is limited because the agglomerates become too sticky to handle if too much liquor is applied to them. However, if the application of the film and seed is repeated several times, a considerably greater amount of liquor can be crystallized. Moreover, recycling of both agglomerates and seed is necessary to promote crystallization at a rate which will decrease the total so-called in process time of a predetermined amount of the liquor, to a minimum. The entire crystallizing, conditioning and grinding operation may be carried out in as little time as 5 hours.

The process of my invention is very advantageous in that it requires only a short time to carry out, the equipment is simple, takes up little space, and operational and maintenance costs are low. One of its main advantages is that it may be operated on a continuous basis.

The invention will be further illustrated by the accompanying drawing and the description which follows. However, it is not intended to limit the invention thereby.

In the drawing, which illustrates my invention diagrammaticaly, the numeral 1 represents a supply of the dextrose liquor. In a typical embodiment, this liquor had a density of 43.5 B., a dextrose equivalent of 94.5 percent, dex trose content of about 90 percent, and temperature of 80 C. The liquor is fed to a dosing pump 2, and then, optionally but preferably, into an agitator 3 wherein the liquor is agitated or whipped to incorporate air into said Table II shows temperatures and moisture contents obtaining in a two-stage coating process wherein the amount of liquor and sed in each stage was the same as hereinabove described.

5 TABLE 11 liquor which increases the total surface within the mass resulting in an accelerated rate of crystallization. The & i RunB liquor is next sprayed, by means not shown, onto ag- C. Percent 0. Percent glomerates of dextrose crystals which may be obtained H20 H20 from a previous run. These agglomerates, in the afOrfl- 1O 4 1 ti $9 17 g? 17 mentioned embodiment, having a temperature of 23 t gigf g f gfi ggaigg 25 ;j;5" 23 ""f 25 C. are fed by means of a shaker gutter 4 into a slantissl g g t l qu og- 40 -22 38 10.28 ing ribbon conveyor unit 5. At the outlet of 4, the ag- 30 M2 31 M0 glomerate? are sprayed with the liquor from by means 26 9. 76 27 9.38 off small ets, not showgndThe agglltlmerates m the rug i gl t fi i i condiigi-flplg ggg 3% re erred to consisted o extrose y rate crystas an F 8 at 1111 an ymg 2 had a diameter of 2.5 to 3.5 mm., and a moisture content Ema} product 26 26 of about 9 percent. The temperature of the wetted ag- I claim: glomerates was about 40 C. at this stage. The amount 1. A process for obtaining dextrose crystals consisting of dextrose liquor sprayed onto the agglomerates was essentially of dextrose hydrate crystals, from a liquor about 20 percent, by weight, dry basis. The wetted agsupersaturated with respect to dextrose and containing glomerates are conveyed forward in conveyor 5 and, as about 75 to about 88 percent, dry substance, which comthey are moved forward, they are coated with dextrose prises seed by means of a seed distributor 6 which consists of (a) forming a thin layer of said liquor on agglomerates a shaker gutter. The amount of seed used in the run was of dextrose crystals, about 20 percent, by weight, of the agglomerates, dry (b) contacting the resultant wetted agglomerates with basis. The coated agglomerates are transferred from the discrete dextrose particles whereby the thin layer of conveyor 5 into another slanting ribbon conveyor 7 whereliquor begins to crystallize substantially instantain they are mixed, for about 15 to 20 minutes, to permit neously and the agglomerates become free-flowing and substantially all of the dextrose in the liquor to crystallize, 30 substantially free of stickiness; resulting in agglomerates which are dry and substantially the temperature of said agglomerates undergoing treatfree of stickiness. The temperature of the agglomerates ment in steps (a) and (b) being maintained within the was maintained at about 30 C. during the mixing operarange of 15 to 45 C., said dextrose crystals in said tion. Cooling air from unit 8 is used in both units 6 and agglomerates of step (a) and the dextrose particles of 7 to maintain the temperature at the desired level. step (b) being predominantly in hydrate form.

The dry agglomerates are then fed into a conditioning 2. Process according to claim 1 wherein said liquor is tube 9 where, in this run, they were held with slow agitaagitated with air before forming said thin layer on said tion for about 2.5 hours to permit completion of the agglomerates of step (a). crystallization and to allow any anhydrous crystals 3. Process according to claim 1 wherein the said present to be converted to the hydrate forrn. Cooling air agglomerates from step (b) are subjected to conditioning is introduced at 10 to maintain the temperature at the at a temperature of about 15 to about 30 C., while the desired level which in this run was 26 C. moisture content of the agglomerates is maintained at a The agglomerates are passed through a calibrating roll value of about 8.5 percent to about 13 percent to com- 12 and sitter 13. About 60 percent of the agglomerates plete crystallization of said liquor and to convert substanis returned to the process at 4. The remainder is ground tially all of the anhydrous crystals in the agglomerates to in mill 14 and dried in dryer 15 to a moisture content the hydrate form. of about 9 percent. The dried material is screened at 16. 4. Process according to claim 1 wherein said agglomer- A portion of the screened material is returned to the ates in step (a) have a diameter not exceeding about process for seed, at 6. The tailings are reground at 14. 10 mm.

The third portion is packed in bags at 17. The final prod- 5. Process according to claim 4 wherein the final uct consisted of dextrose hydrate crystals. agglomerates are ground to a predetermined size, and a In another embodiment, the steps of spraying the liquor portion of these is recycled. onto the agglomerates and then coating with seed were 6. Process according to claim 1 wherein the said repeated three times before the agglomerates were fed agglomerates from step (b) are subjected to conditioning into the conditioning tube 9. in an atmosphere having a relative humidity within the Table I shows the amount of liquor and seed used in range of about to percent and a temperature of a run wherein triple coating was used. about 15 to about 30 C. to complete crystallization of TABLE I Kg. Recycled Kg. Kg. Percent Kg. Agglom- Seed Liquor DS crates Y iifsi 91.5 13.633

Ratio '2. 04 /1 said liquor and to convert substantially all of the anhydrous crystals present in the agglomerates to the hydrate form.

7. Process according to claim 6 wherein said liquor is agitated with air before forming said thin layer on said agglomerates of step (a).

8. Process according to claim 7 wherein said conditioning covers a period of duration within the range of about 2 to 4 hours.

9. Process according to claim 1 wherein the amount of liquor sprayed onto the agglomerates in step (a) is about to about 33 percent, by weight, of the agglomerates, dry basis, and the amount of dextrose particles used in step (-b) is about 20 to 33 percent, by weight, of the wetted agglomerates, dry basis.

10. Process according to claim 9 wherein the temperature of said agglomerates being treated in step (a) is about 15 to C. and that of said liquor is about to C.

11. Process according to claim 9 wherein steps (a) and (b) are repeated successively.

12. Process according to claim 9 wherein the said agglomerates from step (b) are subjected to conditioning in an atmosphere having a relative humidity within the range of about 70 to percent and a temperature of References Cited UNITED STATES PATENTS 988,261 3/1911 Griere 12758 1,708,940 4/ 1929 Daly l2758 2,369,231 2/ 1945 Harding 12716 2,954,306 9/1960 Bond et al. 127-30 X 3,239,378 3/1966 Opila 12730X 3,265,533 8/1966 Meisel 127-38 FOREIGN PATENTS 567,181 12/ 1958 Canada.

MORRIS O. WOLK, Primary Examiner.

D. G. CONLIN, Assistant Examiner. 

1. A PROCESS FOR OBTAINING DEXTROSE CRYSTALS CONSISTING ESSENTIALLY OF DEXTROSE HYDRATE CRYSTALS, FROM A LIQUOR SUPERSATURATED WITH RESPECT TO DEXTROSE AND CONTAINING ABOUT 75 TO ABOUT 88 PERCENT, DRY SUBSTANCE, WHICH COMPRISES (A) FORMING THIN LAYER OF SAID LIQUOR ON AGGLOMERATES OF DEXTROSE CRYSTALS, (B) CONTACTING THE RESULTANT WETTED AGGLOMERATES WITH DISCRETE DEXTROSE PARTICLES WHEREBY THE THIN LAYER OF LIQUOR BEGINS TO CRYSTALLIZE SUBSTANTIALLY INSTANTANEOUSLY AND THE AGGLOMERATES BECOME FREE-FLOWING AND SUBSTANTIALLY FREE OF STICKNESS; THE TEMPERATURE OF SAID AGGLOMERATES UNDERGOING TREATMENT IN STEPS (A) AND (B) BEING MAINTAINED WITHIN THE RANGE OF 15 TO 45*C., SAID DEXTROSE CRYSTALS IN SAID AGGLOMERATES OF STEP (A) AND THE DEXTROSE PARTICLES OF STEP (B) BEING PREDOMINANTLY IN HYDRATE FORM. 